“Sadistic and violent” online gangs of mostly teenage boys are committing crimes, including child abuse and extremism, the National Crime Agency (NCA) has warned.

Reports from technology companies relating to young men using so-called “com networks” increased six-fold between 2022 and 2024, the agency said.

Members use “extreme coercion” to manipulate victims, who are often children and include girls as young as 11, into “harming or abusing themselves, their siblings or pets”, it added.

Graeme Biggar, the NCA’s director general, said the agency was concerned about the “egregious harms and the growing caseload we are seeing from this threat”.

“We’re seeing the same online deception techniques used to extort data from companies stolen in cyber breaches also being used to coerce vulnerable girls into harming themselves or other family members,” he said.

“The level of social networking, the pursuit of notoriety within the networks, and the speed of moving to the most extreme harms, is new and shocking.”

The NCA’s annual national strategic assessment, published on Tuesday, said the groups “routinely share harmful content and extremist or misogynistic rhetoric”.

Some members of these online networks have already been convicted of crimes in the UK or are under investigation, the agency found.

Mr Biggar said the gangs are “collaborating at scale to inflict, or incite others to commit, serious harm”.

“These groups are not lurking on the dark web, they exist in the same online world and platforms young people use on a daily basis,” he added.

In January, Cameron Finnigan, 19, from West Sussex, was jailed for his involvement in what police described as a Satanist terror network targeting children for sexual blackmail.

Police searched his home in March last year and found swastikas, satanic symbols, knives.

Officers also found extreme child abuse material and a guide on how to carry out a mass casualty terror attack on his digital devices.

The NCA on Tuesday identified Finnigan as part of a “deeply concerning” trend of teenage boys participating in these groups.

Mr Biggar urged parents and carers to speak to children about what they are doing online.

James Babbage, the NCA’s director general of threats, described ‘com’ networks as “the online equivalent of urban street gang committing crimes to make money cause fear and harm and gain notoriety”.